1. Field of the Invention
The present invention relates to an electron microscope of scanning type, transmission type, or the like and its operating method, and a computer-readable medium storing instructions for operating an electron microscope.
2. Description of the Related Art
At present, as the magnifying observation equipment for magnifying a micro object, it is utilized that each of an optical microscope and a digital microscope use an optical lens, and the electron microscope uses an electron lens, etc. The electron microscope can design electro-optically the image forming system like the optical microscope by refracting arbitrarily the electron traveling direction. As the electron microscope, in addition to the transmission type that focuses the electron passed through the specimen or the specimen by using the electron lens, there are the reflecting type, the scanning type, the surface emission type (field ion microscope), etc. The reflecting-type electron microscope focuses the electron being reflected from a surface of the specimen. The scanning-type electron microscope scans the converged electron beam on the surface of the specimen and focuses the secondary electron being emitted from each scanning point. The surface emission-type electron microscope focuses the electron being emitted from the specimen by heating or ion irradiation.
The scanning electron microscope (SEM) is such a system that observes mainly a surface mode of the specimen by detecting the secondary electron or the reflection electron being generated when a narrow electron beam (electron probe) is irradiated onto the specimen as the object by each detector such as the secondary electron detector, the reflection electron detector, or the like, and then displaying the image on a display screen such as the cathode-ray tube, the LCD, or the like. On the other hand, the transmission electron microscope can observe mainly an internal structure of the substance by passing the electron beam through a thin film specimen to get the electrons being scattered or diffracted by atoms in the specimen at that time as the electron diffraction pattern or the transmission electron-microscope image.
When the electron beam is irradiated onto the solid specimen, such electron beam passes through the solid by the energy of the electron. At that time, the elastic collision, the elastic scattering, and the inelastic scattering that causes the energy loss are generated by the interaction between such electron beam and the atomic nucleus and the electron constituting the specimen. The inelastic scattering excites the intranuclear electron of the specimen element, excites the X-ray, etc., or emits the secondary electron to cause the corresponding energy to lose. An amount of emitted secondary electrons is different according to a collision angle. In contrast, the reflection electrons that are scattered backward by the elastic scattering and then emitted again from the specimen are emitted by an amount peculiar to the atomic number. The SEM forms the observation image by detecting the secondary electrons or the reflection electrons that are emitted from the specimen by irradiating the electrons onto the specimen (for example, JP-A-2001-338603).
It is normal that the electron microscope executes the observation in high vacuum, but the electron microscope that is able to execute the observation in low vacuum (e.g., low vacuum SEM) has also been developed (for example, JP-A-2002-289129). The low vacuum observation prevents a charge-up of the specimen, an evaporation of a volatile component, etc. during the observation by lowering a degree of vacuum in the specimen chamber of the electron microscope. Accordingly it is possible to observe the specimen that is difficult to observe in high vacuum by the ordinary high vacuum SEM, such as the specimen that contains a moisture or an oil content, the specimen that emits a large amount of gas, etc.
However, such problems existed that normally the operation of the electron microscope is difficult and that settings becomes more difficult particularly in the low vacuum observation since a parameter of a degree of vacuum is further added. Normally, operating procedures of the electron microscope such as SEM, TEM, etc. are difficult to understand in contrast to other magnifying observation equipments such as the optical microscope, the digital microscope, etc. Although the image observation conditions must be set to observe the image by the electron microscope, many setting/adjusting items are present and these items must be set to the appropriate image observation conditions according to the specimen and the observation purpose, and thus setting the above items bores the beginner. In the low vacuum observation in which a degree of vacuum in the specimen chamber is varied, since a parameter of a degree of vacuum is further added in addition to the normal high vacuum observation, the setting of the image observation conditions, which is difficult even up to date, becomes more difficult. For this reason, in many cases the skilled expert operator carried out the operation of the SEM.
In particular, the number of gas molecules is increased in the specimen chamber in the low vacuum observation rather than the normal high vacuum observation. Because a quantity of signal is reduced because of collision of the electrons against the gas molecules, the image formation becomes difficult rather than the normal case. It is desired that, since a degree of vacuum that is excessively lowered makes the observation difficult, the observation should be carried out even in low vacuum while increasing a degree of vacuum as highly as possible. Therefore, while changing a degree of vacuum and other conditions within allowable ranges, the observation must be carried out in the low vacuum observation under threshold conditions that permit the observation. In order to set the optimum conditions, the operator must know how respective parameters such as a degree of vacuum, etc. exert an influence upon the image. As a result, if the operator is not the skilled person, it is difficult for such operator to set such optimum conditions.
Also, the adjustment must be repeated while repeating the trial and error until the optimum conditions are obtained. In this case, since the image is picked up in the low vacuum observation while changing a degree of vacuum, such a problem existed that the operation for changing a degree of vacuum takes a lot of time. Because the air in the specimen chamber must be sucked/evacuated by the pump, or the like to control a degree of vacuum, it takes a time to some extent until an interior of the specimen chamber comes up to a desired degree of vacuum. Therefore, if it is tried to optimize the conditions by the trial and error, a degree of vacuum must be varied many times. Thus, the operator must wait while operating the pump every time until a degree of vacuum reaches a designated level. In this manner, the change of a degree of vacuum in the low vacuum observation requires a long time in comparison with other parameters, and it is impossible to carry out the observation until the change is completed. Also, since the image must be formed actually under the designated conditions and then the operator must judge the conditions by looking at the resultant observation image, such operator could not go away from the electron microscope during the operation to take a time and labor, and thus a working efficiency became low. As described above, the setting operation of the image observation conditions was difficult in the low vacuum observation rather than the normal electron microscope.